Medical devices (MDs) have been used to detect events associated with a range of medical conditions. Upon a positive event detection, MDs may provide a range of responsive actions such as logging or recording, warning, providing treatment, or summoning assistance. MDs may be implantable, external, or may include both implantable and external components.
For epilepsy patients, MDs having seizure detection algorithms have been proposed. Detection may be based upon autonomic and/or neurologic data from the patient. Treatment therapies may be initiated in response to detection to prevent, terminate, or reduce the severity of seizures in patients with epilepsy, and may include, e.g., drug infusion via an implanted pump, and electrical stimulation therapies such as deep brain stimulation (DBS) or vagus nerve stimulation (VNS).
Electrical stimulation therapies applied in response to detection of a seizure is referred to as closed-loop stimulation. Open-loop stimulation, in contrast, the electrical signal is applied to the target tissue according to specified parameters for a defined period of time (e.g., 30 seconds), referred to as the on-time, after which the electrical signal ceases for a defined period of time (e.g., 5 minutes), referred to as the off-time. In addition to open-loop and closed-loop stimulation, some MDs allow stimulation to be initiated manually by a patient or caregiver (e.g., by a magnet signal provided transcutaneously to an IMD). Combinations of open-loop, closed-loop and manual stimulation may also be permitted.
Algorithms to detect epileptic seizures (or an increased risk of a seizure, either or both of which may constitute a “seizure event”) have been proposed based upon one or more cardiac parameters such as heart rate or heart rate variability. See, e.g., U.S. Pat. No. 5,928,272, U.S. Pat. No. 6,341,236, U.S. Pat. No. 6,671,556, U.S. Pat. No. 6,961,618, U.S. Pat. No. 6,768,969, U.S. application Ser. No. 12/770,562, U.S. application Ser. No. 12/771,727, and U.S. application Ser. No. 12/771,783, which are hereby incorporated herein by reference. Current detection algorithms, however, have unacceptably high rates of false positive detections (i.e., detecting a seizure event when no seizure has occurred) and false negatives. There is a need for improved algorithms having both greater sensitivity (ability to detect seizures) and specificity (detecting only seizure events).